The present invention was made in the course of applicant's design and development of a substitute for a certain type of drop forged chain which is used in trolley conveyors. U.S. Pat. Nos. 1,901,850 and 1,962,531 show such conveyors. Such chain operates in a generally horizontal loop over a number of sprockets and below a track. Wheeled brackets hang from the track and support the chain at regular intervals and the individuals articles to be conveyed. The track is also inclined as required to lift or lower the articles in the course of movement. As a consequence, it is necessary that the chain may flex in a vertical plane as well as articulate in the horizontal plane.
The drop forged chain referred to includes center links and pin links in the form of extended loops with lengthwise slots and pins extending therethrough. The pins are T-headed and their opposite projections are retained in the sides of the pin links. While the ends of the center links maintain the spacing between the pin links, the narrower mid-section of the center link allows any of the several links to be assembled or disassembled in a known manner. Specifically, with the center link mid-section between the ends of two pin links, the latter may be brought closer together to release the pin and allow it to be turned 90.degree. and withdrawn through the aligned slots. For assembly, the pin may be inserted through the slots and turned 90.degree.. With the wider end of the center link again disposed between the ends of the two pin links, the pin is again retained as provided for.
A typical chain of this type may have a pitch of six inches. A smaller size has a pitch of three inches, a tensile strength of 24,000 pounds and a working load rating of 2800 pounds. A main reason for this relatively low load rating is the wear of the pin and the center link which results from their sliding movement under load when the chain flexes in a vertical plane.
Applicant's substitute chain includes links of a similar configuration so as to be interchangeable therewith but is of a molded plastic construction for less cost and corrosion resistance. A homopolymer acetal resin sold under the trademark "Delrin" is an exemplary material but provides a chain having a tensile strength of only 3,000 pounds and a proportionately low load rating for much the same reason, namely the extremely high corner loading imposed on the center links by the pins when the chain flexes as required.
While the object of the present invention has been to overcome this problem in this type of chain, the present invention is also expected to provide an improvement in any number of difference types of chain where flexing normal to normal articulation is required.